Transcript Sunelle Otto

Probing the field of Radio
Astronomy with the SKA and the
Hartebeesthoek Radio
Observatory:
An Engineer’s perspective
Sunelle Otto
Hartebeesthoek Radio Astronomy
Observatory (HartRAO)
July 2011
Outline
• Introduction
• The Square Kilometre Array
- Background, Pathfinders ,
Key Science Projects, System design
• Hartebeesthoek Radio Astronomy Observatory
- Background, Research work
• Conclusion
Introduction
• MSc (Electronic Engineering)
at Stellenbosch University
- thesis work on SKA
• Intern at HartRAO
(Hartebeesthoek Radio
Astronomy Observatory)
- research work
Stellenbosch University
The Square Kilometre Array
Background
• Square Kilometre Array (SKA)
• largest, most sensitive
radio telescope
• thousands of small dishes and
aperture arrays
• total collecting area of 1 km²
• South Africa vs. Australia
• International project
• smaller projects to assist in research
• SKA pathfinders to demonstrate the
technologies
SKA configuration design
The Square Kilometre Array
Pathfinders
• MeerKAT (South Africa)
• Started with the XDM
(eXperimental Development
Model)
• 15m diameter parabolic
reflector dish
• 7 horn cluster feed
• Located at HartRAO
XDM antenna
7 horn feed
The Square Kilometre Array
Pathfinders
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KAT-7 (Karoo Array Telescope)
Array of 7 parabolic reflector antennas each 12m in diameter
Wide-band single pixel feeds (WBSPFs)
Demonstrates working of an interferometer
KAT-7
The Square Kilometre Array
Pathfinders
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MeerKAT: final phase of KAT
64 offset Gregorian antennas
13.5m diameter
unblocked aperture
multiple receiver systems
MeerKAT antenna design
(credit: SKA fact sheet 1: MeerKAT,
June 2011, www.ska.ac.za)
The Square Kilometre Array
Pathfinders
• ASKAP (Australian Square
Kilometre Array Pathfinder)
• Goal: 36 parabolic reflectors
• each 12m diameter
• Phased array feeds (PAFs)
• Multiple beam formation
capability
ASKAP
Phased Array Feed
The Square Kilometre Array
Pathfinders
• EMBRACE (Electronic Multi Beam
Radio Astronomy Concept)
• THEA (Thousand Element Array)
• Dense Aperture Arrays
• Vivaldi antennas
Dense Aperture Array
• LOFAR (Low Frequency Array)
• Sparse Aperture Arrays
• Dipole antennas
Sparse Aperture Array
The Square Kilometre Array
Key Science Projects
• Science observations requested by the radio astronomers, SKA drivers
• The Cradle of Life
- terrestrial planet formation, molecular chemistry and the search for
intelligent life
• Strong-Field Tests of Gravity using Pulsars and Black Holes
- Pulsar search and timing, test relativistic gravity and detect gravitational
waves
• The Origin and Evolution of Cosmic Magnetism
- map the origin and evolution of magnetic fields
• Galaxy Evolution, Cosmology and Dark Matter
- study the cosmic evolution of HI (neutral hydrogen), dark energy and dark
matter
• Probing the Dark Ages
- study the epoch of reionisation (EoR)
The Square Kilometre Array
System design
Hartebeesthoek Radio Astronomy
Observatory (HartRAO)
Background
• HartRAO is the only major radio astronomy observatory in Africa;
KAT-7 is still in testing,
MeerKAT in design phase
• 26m radio telescope
• Single dish observations
• VLBI (very large baseline
interferometry)
26 m Telescope at HartRAO
HartRAO – research work
Pointing model
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Telescope needs to find and track sources accurately
Need good pointing model
Pointing scans for various sources
Data used to improve the pointing model
Hour Angle pointing error vs HA
Declination pointing error vs HA
HartRAO – research work
Rubidium and Hydrogen Maser clocks
• Hydrogen Maser
- frequency standard, accurate timing
• Rubidium clock, GPS10RB
- Less accurate, corrects time by periodically comparing it with
GPS (global positioning system) satellites
• Measure difference between :
 Maser and Rubidium clock times
 Maser and GPS clock times
• performance of Rubidium
HartRAO – research work
Rubidium and Hydrogen Maser clocks
• slope in the graph : frequency drift of the Maser clock
• Phase noise: due to GPS signal path variations
through the atmosphere
Rubidium vs Hydrogen maser
GPS vs Hydrogen maser
HartRAO – research work
Rubidium and Hydrogen Maser clocks
• 5min averages made, see how Rubidium follows the GPS
• Look at frequency stability:
Rubidium has short term stability, while GPS has long term
stability
5min averages (Rubidium, GPS)
Frequency stability (Rubidium, GPS)
HartRAO – research work
Building a 1.4GHz receiver
• Receiver for a satellite TV antenna
• 3m diameter
• Testbed for demonstrating practical
radio astronomy at school and
University level
• Cylindrical waveguide
horn feed with
choke ring
3 m dish with 1.4 GHz receiver
HartRAO – research work
H₂0 Maser in Orion KL
• Observations of H₂0 Masers in
the Orion KL source region
• 22GHz
• March 2011 to present
• Why? Flares occurred in
1984, 1998
• Flux density reached millions
of Janskys
Orion KL
HartRAO – research work
H₂0 Maser in Orion KL
• Average spectrum
• Flux Density:
80,000 Jy
• compare with data
from 2007 when
maser was not flaring
(light blue)
Average spectrum (lcp and rcp added)
HartRAO – research work
H₂0 Maser in Orion KL
• Time series plot at main peak velocities
Time series plots (lcp)
Conclusion
• The Square Kilometre Array
- Pathfinders
- Key Science Projects
- System design
• Hartebeesthoek Radio Astronomy Observatory
- Pointing model
- Rubidium and Hydrogen Maser clocks
- 1.4GHz receiver
- H₂0 Maser in Orion KL
Thank you!